Logical Reasoning

PT106 · S2 · Q11 John works five days each week

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John works five days each week except when on vacation or during weeks in which national holidays occur.

Conclusion

John must have worked in the insurance company on Mon - Thurs last week.

Evidence

If it isn't a national holiday and not a vacation week, then John works five days each week.

Last week was neither a holiday nor a vacation week.

He works four days a week at an insurance company. On Friday he works as a blacksmith.

Evaluate

The evidence establishes that John worked five days last week. And we know that four of those five days involved working at an insurance company. But there's no reason we need to think those four days were Mon - Thu.

First of all, just because John works as a blacksmith on Fridays, he might also work at an insurance company on Friday. Nothing in here says he only works one job per day.

Secondly, even if we accepted that John only works as a blacksmith on Friday, that still leaves Saturday, Sunday, Monday, Tuesday, Wednesday, and Thursday as the six remaining options for the four insurance days.

Goal

The argument is assuming that . And it's assuming "John doesn't work on the Sat / Sun".

11.

Which one of the following is an assumption on which the argument depends?

  1. John never takes a vacation

    Too Strong: never

    This argument is about a week in which John isn't on vacation, so the argument isn't assuming anything about what John does when he is on vacation.

    2% picked this

  2. Every day last week that

    Out of Scope: entire workday

    The wording only talks about whether or not he works on a given day. It doesn't ever get into this new nuance of whether it's a partial vs. entire workday. At first I thought maybe this answer was aloofly getting at the "what if he worked at two jobs on Friday" objection, but it would need to be much more specifically tailored to that kind of language. If we negate this answer and say, "At least one day last week that John worked, he only worked for 80% of the workday", that wouldn't weaken anything.

    2% picked this

  3. John does not take vacations

    Premise Salad

    This is just blending concepts from the premises, but it has nothing to do with what needs to be assumed in order to draw the conclusion that he must have worked M/Tu/W/Th. If we negated this and said, "John does sometimes take vacations during holiday weeks", that wouldn't weaken the argument at all, especially since last week was neither a vacation week nor a holiday week.

    3% picked this

  4. Correct

    Last week John worked neither

    Why this is right

    The author is thinking, "Okay, he worked 5 days, 4 of them at insurance. Friday is gone because of blacksmithing, so he must have worked Mon/Tu/Wed/Thu." But why does it have to be those four days? Couldn't one or two of his four days been a Saturday or Sunday? The author is assuming "no". If we negated this answer, we'd be saying "John worked on Sat and/or Sunday of last week". That would badly weaken the argument, because there would be no reason to think that his four days at the insurance company were M / Tu / W / Th, if we knew that one or two of the five days he worked last week was a Saturday or Sunday.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    75% picked this

  5. There were no days last

    Too Strong: no days

    Man, this is tempting, because this relates to our other objection, "What if John doubled-up on Friday?" However, this answer in that case should sound like this: "On Friday, John did not both work in the insurance company and also work as a blacksmith." This answer becomes too strong by precluding that from happening on no days. It's not an objection to the argument if, on Monday, John worked at both insurance and blacksmith. It's only an objection if it happened on Friday, since the author is using "blacksmith on Friday" to rule out "insurance on Friday". Does John only work at the blacksmith on Friday? We don't know. We were never told he works only one blacksmith shift per week. We were never told that he works as a blacksmith only on Friday. So the author doesn't have to believe that John never doubled-down on insurance/blacksmith on Mon / Tu / Wed / Thu. She only needs to assume he didn't double down on Friday.

    17% picked this

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